Friday, April 24, 2015

Brain-Immune Cross-Talk May Build Resilience Against Stress

We
tend to assume our thoughts and feelings are controlled almost
exclusively by our brains.

But peripheral systems, such as our
hormonal and immune systems also influence how we think, feel and
behave.

Communication between the brain and rest of the body goes both ways.
Psychological stress and stress hormones alter the status of the immune
system. In turn, an agitated immune system will impact brain function
and structure.

A team of researchers from NIH–DHHS facility in Bethesda Maryland
recently explored the idea of bidirectional brain-immune communication
to see if cells of the adaptive immune system retain the memory of
psychosocial stress and thereby alter mood states and brain function.

To generate ‘stressed mice’, pairs of mice were housed together: a
dominant aggressive mouse with an ‘intruder’ who became stressed and
‘socially defeated’. Lymphocytes (a type of immune cell) were isolated
from the stressed mouse and injected into another healthy ‘non-stressed
out’ host mouse.

Unexpectedly, the stressed immune cells didn’t confer anxiety and depression, instead they appeared to protect against stress. They built resilience in the host mouse. The recipient mice showed:

less anxiety and depression-related behaviours and increased sociability

reduced pro-inflammatory cytokine levels in the blood

increased cell proliferation in the hippocampus (of the like seen with anti-depressant use)

Remarkably, the behaviours and biochemical profiles associated with stress were reversed in the mice receiving cells from stressed donors. As the authors say “In effect, equilibrium was restored.” These results suggests that psychological stress can modify adaptive immune cells in a long-lasting manner that may boostresilience to stress.

The team wonders if differences in the adaptive immune system may
account for different susceptibilities to stress and resilience, and
could potentially be useful in identifying at-risk individuals. Finally,
they suggest the immune system could be a viable target for
antidepressant therapies.